added insert_single API (issue #122)

tests/parallel_hash_set_test.cc

@@ -0,0 +1,36 @@
+#ifndef THIS_HASH_SET
+    #define THIS_HASH_SET  parallel_flat_hash_set
+    #define THIS_TEST_NAME ParallelFlatHashSet
+#endif
+
+#include "flat_hash_set_test.cc"
+
+namespace phmap {
+namespace priv {
+namespace {
+
+TEST(THIS_TEST_NAME, ThreadSafeContains) {
+    // We can't test mutable keys, or non-copyable keys with ThisSet.
+    // Test that the nodes have the proper API.
+    using Set = phmap::THIS_HASH_SET<int>;
+
+    {
+        // --------------------
+        // test emplace_single
+        // --------------------
+        Set m = { {1}, {11} };
+ 
+        // emplace_single insert a value if not already present, else removes it
+        for (int i=0; i<12; ++i)
+            m.emplace_single(i, [i](const Set::constructor& ctor) { ctor(i); });
+        EXPECT_EQ(m.count(0), 1);
+        EXPECT_EQ(m.count(1), 0);
+        EXPECT_EQ(m.count(2), 1);
+        EXPECT_EQ(m.count(11), 0);
+    }
+
+}
+
+}  // namespace
+}  // namespace priv
+}  // namespace phmap